Authorities in Kuwait have warned they will take a tougher line against anti-government demonstrators defying bans on protest gatherings.

Thursday's warning came as the Gulf nation's opposition leader Mussallam al-Barrak was released on bail after a night of violent protests against his detention that left dozens hurt, his lawyer and an AFP photographer said.

Kuwaiti media reported that al-Barrack, a former member of parliament under investigation for allegedly insulting Kuwait's emir, paid more than $35,500 before he was granted bail.

The interior ministry said forces will "firmly" confront any new demonstrations, adding that a "number" of protesters have been arrested, including a driver who allegedly tried to run over four policemen late on Wednesday.

Opposition groups held an emergency meeting in the wake of the night-long clashes, condemning the government's "barbaric suppression" of peaceful demonstrations.

They said Kuwait was becoming a police state.

Kuwait last week banned any public gathering of more than 20 people in attempts to quash growing protests led by opposition factions that include Islamists.

The protesters are seeking to reclaim control of parliament in elections planned for December 1.

Pivotal moment

The outcome is seen as a pivotal moment in Kuwait's political showdowns. A victory for the Islamists and their allies could bring even more pressures on the Western-backed ruling family, which has so far turned back demands for stricter Muslim social codes in Kuwait.

Kuwait's deepening political crisis could bring further rifts in one of Washington's most important Gulf allies, which now hosts the bulk of US ground forces in the region following US withdrawal from Iraq.

Kuwait has the most politically empowered parliament among the Gulf Arab states, with opposition legislators often directly challenging government officials over alleged corruption and power abuses.

Activists said that dozens of people, especially children, were rushed to hospital after inhaling gases as riot police extensively used stun grenades and tear gas cannisters in their attempt to disperse the protesters.

Opposition groups are to hold an emergency meeting on Thursday following the violent clashes outside the prison, a former MP and activists said.

Oil-rich Kuwait has not faced widespread unrest since the Arab Spring uprisings erupted last year across the Middle East.

However, political battles and labour upheavals have stalled many development plans and rewritten the rules on political dissent.